Added restrictions when relaying file list requests

1) Each relay request expires after 5 seconds, after which nodes will stop relaying it, preventing any kind of infinite loop. So it has to reach the destination peer within 5 seconds. This should be fine, because the original peer's request would timeout anyway, so there's nothing to be gained by continuing to relay it.

2) Each relay request stops being forwarded after 3 "hops" - i.e. once it has been relayed through 3 different peers, it will no longer be transmitted any further. If we assume that each node has 16 connections, that allows it to reach a theoretical maximum of 4096 peers in 3 hops. In practice it will be less, and may not reach everyone due to peer "islands". But it will automatically retry a few times on a timer, so should hopefully find what it needs eventually. Plus, it still has the ability to make a direct connection to anyone hosting the data, as long as they are port forwarded.

src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileListManager.java

@@ -56,6 +56,12 @@ public class ArbitraryDataFileListManager {
     private Map<String, Triple<Integer, Integer, Long>> arbitraryDataSignatureRequests = Collections.synchronizedMap(new HashMap<>());
 
 
+    /** Maximum number of seconds that a file list relay request is able to exist on the network */
+    private static long RELAY_REQUEST_MAX_DURATION = 5000L;
+    /** Maximum number of hops that a file list relay request is allowed to make */
+    private static int RELAY_REQUEST_MAX_HOPS = 3;
+
+
     private ArbitraryDataFileListManager() {
     }
 
@@ -223,6 +229,11 @@ public class ArbitraryDataFileListManager {
         byte[] signature = arbitraryTransactionData.getSignature();
         String signature58 = Base58.encode(signature);
 
+        Long now = NTP.getTime();
+        if (now == null) {
+            return false;
+        }
+
         // If we've already tried too many times in a short space of time, make sure to give up
         if (!this.shouldMakeFileListRequestForSignature(signature58)) {
             // Check if we should make direct connections to peers
@@ -238,7 +249,7 @@ public class ArbitraryDataFileListManager {
         LOGGER.debug(String.format("Sending data file list request for signature %s...", Base58.encode(signature)));
 
         // Build request
-        Message getArbitraryDataFileListMessage = new GetArbitraryDataFileListMessage(signature);
+        Message getArbitraryDataFileListMessage = new GetArbitraryDataFileListMessage(signature, now, 0);
 
         // Save our request into requests map
         Triple<String, Peer, Long> requestEntry = new Triple<>(signature58, null, NTP.getTime());
@@ -386,8 +397,8 @@ public class ArbitraryDataFileListManager {
         GetArbitraryDataFileListMessage getArbitraryDataFileListMessage = (GetArbitraryDataFileListMessage) message;
         byte[] signature = getArbitraryDataFileListMessage.getSignature();
         String signature58 = Base58.encode(signature);
-        Long timestamp = NTP.getTime();
-        Triple<String, Peer, Long> newEntry = new Triple<>(signature58, peer, timestamp);
+        Long now = NTP.getTime();
+        Triple<String, Peer, Long> newEntry = new Triple<>(signature58, peer, now);
 
         // If we've seen this request recently, then ignore
         if (arbitraryDataFileListRequests.putIfAbsent(message.getId(), newEntry) != null) {
@@ -446,7 +457,7 @@ public class ArbitraryDataFileListManager {
         if (hashes.size() > 0) {
 
             // Update requests map to reflect that we've sent it
-            newEntry = new Triple<>(signature58, null, timestamp);
+            newEntry = new Triple<>(signature58, null, now);
             arbitraryDataFileListRequests.put(message.getId(), newEntry);
 
             ArbitraryDataFileListMessage arbitraryDataFileListMessage = new ArbitraryDataFileListMessage(signature, hashes);
@@ -462,11 +473,31 @@ public class ArbitraryDataFileListManager {
             boolean isBlocked = (transactionData == null || ArbitraryDataStorageManager.getInstance().isNameBlocked(transactionData.getName()));
             if (Settings.getInstance().isRelayModeEnabled() && !isBlocked) {
                 // In relay mode - so ask our other peers if they have it
-                LOGGER.debug("Rebroadcasted hash list request from peer {} for signature {} to our other peers", peer, Base58.encode(signature));
-                Network.getInstance().broadcast(
-                        broadcastPeer -> broadcastPeer == peer ||
-                                Objects.equals(broadcastPeer.getPeerData().getAddress().getHost(), peer.getPeerData().getAddress().getHost())
-                                ? null : message);
+
+                long requestTime = getArbitraryDataFileListMessage.getRequestTime();
+                int requestHops = getArbitraryDataFileListMessage.getRequestHops();
+                getArbitraryDataFileListMessage.setRequestHops(++requestHops);
+                long totalRequestTime = now - requestTime;
+
+                if (totalRequestTime < RELAY_REQUEST_MAX_DURATION) {
+                    // Relay request hasn't timed out yet, so can potentially be rebroadcast
+                    if (requestHops < RELAY_REQUEST_MAX_HOPS) {
+                        // Relay request hasn't reached the maximum number of hops yet, so can be rebroadcast
+
+                        LOGGER.info("Rebroadcasting hash list request from peer {} for signature {} to our other peers... totalRequestTime: {}, requestHops: {}", peer, Base58.encode(signature), totalRequestTime, requestHops);
+                        Network.getInstance().broadcast(
+                                broadcastPeer -> broadcastPeer == peer ||
+                                        Objects.equals(broadcastPeer.getPeerData().getAddress().getHost(), peer.getPeerData().getAddress().getHost())
+                                        ? null : getArbitraryDataFileListMessage);
+
+                    }
+                    else {
+                        // This relay request has reached the maximum number of allowed hops
+                    }
+                }
+                else {
+                    // This relay request has timed out
+                }
             }
         }
     }

src/main/java/org/qortal/network/message/GetArbitraryDataFileListMessage.java

@@ -1,5 +1,7 @@
 package org.qortal.network.message;
 
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
 import org.qortal.transform.Transformer;
 
 import java.io.ByteArrayOutputStream;
@@ -7,20 +9,27 @@ import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 import java.nio.ByteBuffer;
 
+import static org.qortal.transform.Transformer.INT_LENGTH;
+import static org.qortal.transform.Transformer.LONG_LENGTH;
+
 public class GetArbitraryDataFileListMessage extends Message {
 
 	private static final int SIGNATURE_LENGTH = Transformer.SIGNATURE_LENGTH;
 
 	private final byte[] signature;
+	private final long requestTime;
+	private int requestHops;
 
-	public GetArbitraryDataFileListMessage(byte[] signature) {
-		this(-1, signature);
+	public GetArbitraryDataFileListMessage(byte[] signature, long requestTime, int requestHops) {
+		this(-1, signature, requestTime, requestHops);
 	}
 
-	private GetArbitraryDataFileListMessage(int id, byte[] signature) {
+	private GetArbitraryDataFileListMessage(int id, byte[] signature, long requestTime, int requestHops) {
 		super(id, MessageType.GET_ARBITRARY_DATA_FILE_LIST);
 
 		this.signature = signature;
+		this.requestTime = requestTime;
+		this.requestHops = requestHops;
 	}
 
 	public byte[] getSignature() {
@@ -28,14 +37,18 @@ public class GetArbitraryDataFileListMessage extends Message {
 	}
 
 	public static Message fromByteBuffer(int id, ByteBuffer bytes) throws UnsupportedEncodingException {
-		if (bytes.remaining() != SIGNATURE_LENGTH)
+		if (bytes.remaining() != SIGNATURE_LENGTH + LONG_LENGTH + INT_LENGTH)
 			return null;
 
 		byte[] signature = new byte[SIGNATURE_LENGTH];
 
 		bytes.get(signature);
 
-		return new GetArbitraryDataFileListMessage(id, signature);
+		long requestTime = bytes.getLong();
+
+		int requestHops = bytes.getInt();
+
+		return new GetArbitraryDataFileListMessage(id, signature, requestTime, requestHops);
 	}
 
 	@Override
@@ -45,10 +58,25 @@ public class GetArbitraryDataFileListMessage extends Message {
 
 			bytes.write(this.signature);
 
+			bytes.write(Longs.toByteArray(this.requestTime));
+
+			bytes.write(Ints.toByteArray(this.requestHops));
+
 			return bytes.toByteArray();
 		} catch (IOException e) {
 			return null;
 		}
 	}
 
+	public long getRequestTime() {
+		return this.requestTime;
+	}
+
+	public int getRequestHops() {
+		return this.requestHops;
+	}
+	public void setRequestHops(int requestHops) {
+		this.requestHops = requestHops;
+	}
+
 }